The captain of a smuggler ship that capsized off Libya's coast killing up to 950 people made a hasty manoeuvre that resulted in what has been described as the Mediterranean's worst migrant tragedy, Italian prosecutors alleged.

Survivors told investigating authorities their vessel sank after colliding with the King Jacob, a Portuguese-flagged container carrier, which had been dispatched by Italy's Coast Guard to help the migrant boat.

Prosecutors in the Sicilian city of Catania claimed evidence suggests the suspected people trafficker steered his ship towards the approaching rescue vessel and then moved away from the helm to hide himself among the asylum seekers. Doing so, he lost full control of the boat, which eventually crashed into the King Jacob.

According to an earlier reconstruction, the 20m (66ft) vessel overturned because migrants rushed to one side upon seeing an approaching container ship. Investigating authorities told Ansa news agency they now believe both events concurred in causing the incident.

The smuggler ship's captain, named as 27-year-old Tunisian national Ali Malek and a Syrian crew member identified as Mahmud Bikhit, 25, have been arrested.

The pair have been charged with people trafficking and reckless multiple homicide in relation to the disaster.